Random continuous glass mat is increasingly being used in the construction of composite automobile interior trim structures. The random mat is formed by showering molten glass onto a moving conveyor belt. The glass is showered from a rotating head and is directed perpendicular to the direction of movement of the conveyor belt.
In forming automobile interior trim structures, a section of the random mat is typically cut to an appropriate shape (e.g., a door panel) and then draped over a mold surface. A resin is then poured or injected into the mold as part of a resin transfer molding process. The resin process can be, for example, a structural reaction injection molding (SRIM) resin, a low density matt molding resin process or otherwise. The resultant composite part is light-weight yet structurally suitable for various interior trim parts, such as door panels, quarter panels, instrument panels, package trays, and more.
When structures having a fairly complex geometry are needed, the random glass mat must be preformed to the approximate shape of the molding tool. This increases the complexity of manufacturing the trim structures because it typically requires an extra step in which the random mat is compression molded to the approximate shape of the tool. Consequently, other means of manufacturing a glass fiber preform having the properties of random continuous glass mat have been investigated.
One such manufacturing process, known as directed fiber, uses chopped glass fiber and a binder to form a glass fiber preform. In the directed fiber process, chopped glass fibers are sprayed against a screen having the shape of the desired preform. Air is drawn through the screen as the glass fibers are applied to hold the glass fiber onto the screen. Binder is either sprayed over the applied glass fiber or sprayed onto the screen along with the glass fiber. Heat is then applied to cure the binder. The preform is then cooled and remove from the screen. Using chopped glass of one to six inches in length, this process produces a preform having physical properties similar to random continuous glass mat.
Various examples of directed fiber systems are disclosed in U.S. Pat. Nos.: 3,170,197, issued Feb. 23, 1965 to I. G. Brenner; 3,193,440, issued Jul. 6, 1965 to K. A. Schafer; 3,791,783, issued Feb. 12, 1974 to R. L. Damon et al.; 4,061,485, issued Dec. 6, 1977 to C. F. Rimmel; and 5,041,260, issued Aug. 20, 1991 to C. F. Johnson et al.
One disadvantage of the directed fiber process is that it requires the relatively time-consuming step of spraying the chopped glass onto the screen, whether by an operator or robot. Also, because a certain amount of the glass fibers being sprayed does not adhere to the screen, the directed fiber process results in glass being wasted.
Molding processes other than directed fiber that utilize a screen or other porous molding surface have been disclosed. U.S. Pat. No. 3,193,440, issued Jul. 6, 1965 to K. A. Schafer, discloses a process for making laminated articles. In that patent, a screen is dipped into a container of foamed polyurethane fragments as suction is applied to the backside of the screen. Binder is then sprayed and cured. The layer of foamed fragments is then placed in a mold with a preform fiberglass mat for lamination of the two layers. Additionally, Schafer discloses forming a laminate by first applying a layer of glass fibers to the screen, then applying a layer of the foamed polyurethane fragments, and then applying a binder.
There are, however, disadvantages in dipping the screen into the container of fragments. Since the surface of the screen typically has a relatively complex geometry, uniform coating of the screen may not occur, with the portions of the screen located farther from the charge in the container being less likely to have as thick a coverage of the fragments as the closer portions of the screen. Also, such a process is best suited for foamed polyurethane fragments which are lightweight and are therefore easily drawn upward by the airflow through the screen. Glass fibers on the other hand are relatively heavy, making it more difficult to draw them up from the surface of the charge of fiberglass.
Many types of processes that relate generally to forming layers from fragmented materials are known outside of the field of fiber preform fabrication. For example, slush molding has been used to form thermoplastic layers of polyvinyl chloride (PVC). That process uses a mold tool having a solid surface in the shape of the desired part. The mold is preheated and clamped to a powder box containing a charge of dry thermoplastic particles. The mold and powder box are rotated as a single unit until the thermoplastic material is dumped onto the mold surface. A portion of the thermoplastic material attaches and remains on the mold surface while the mold and powder box are rotated together back to their initial position. The mold is disconnected from the powder box and further heated to cause the attached thermoplastic material to fuse together to thereby form a continuous layer of thermoplastic material. An example of the slush molding process is described in U.S. Pat. No. 4,664,864, issued May 12, 1987 to J. M. Wersosky.